When can a meter for measuring milk be used?

The use of a meter for measuring milk is strictly regulated to ensure accuracy and safety in transactions involving dairy products. A meter can only be utilized when it has been checked and approved by the appropriate authority. This approval process typically involves verifying that the meter meets industry standards and regulations, ensuring that it accurately measures the volume of milk being dispensed.

By requiring official checks and approvals, the integrity of measurements is maintained, which is crucial in commercial settings. This ensures fair trade practices and helps to prevent disputes regarding the quantity of milk sold, as both buyers and sellers rely on accurate measurements for their respective benefits.

The other options do not align with the regulations governing the use of milk meters. Simply plugging in the meter does not guarantee correctness, as it must first be verified. There are specific guidelines as to when these devices can be used, rather than leaving it to the operator's discretion. Additionally, usage does not require a timeframe like one year before it can be used; what matters is that it has passed the necessary checks and been approved for use.